1. Field of the Invention
The present invention relates to a process for preparing a die suitable for pressing sheet metal material.
2. Description of the Prior Art
Heretofore, press dies have been prepared by shaping carbon tool steel, alloy steel or die steel and heat-treating the die, or by casting cast iron or a copper-aluminum alloy. In particular, in order to prepare a large-size press die, copper-aluminum alloy having excellent properties of wear resistance, protection against galling and smoothness has been overlaid on a base metal formed by roughly machining a low cost steel, thereby obtaining an economical and excellent metal die.
When carbon tool steel, alloy steel or die steel is used, it is necessary to carry out heat treatments after a rough-machining and a relatively complicated grinding operation. In particular, it is difficult to carry out the grinding of the inner surface of a die having a complicated shape. A casting process is required for cast iron or copper-aluminum alloy. The cast iron has a disadvantage of low wear resistance and the copper-aluminum alloy has a disadvantage of high material cost even though it has excellent properties of wear resistance, protection against galling and smoothness. In the conventional process in which copper-aluminum alloy is welded on the surface of the base metal, it is necessary to roughly machine the inner surface of the die. It is difficult to form a overlaid metal on the inner surface of the die when the shape of die is complicated or the size is small.
In the case of carbon tool steel, alloy steel or die steel, when a blank of stainless steel plate or high tensile steel plate is worked, galling is easily caused in a drawing operation. When the galling occurs, the surface of the pressed product is damaged. It is thus necessary to grind the die so as to repair the galling damage.